Expisoft

Wednesday, October 10, 2007

Then attaching to a process to debug it the default debugging flags is DEBUG_ONLY_THIS_PROCESS, meaning that if the process calls CreateProcess the child process will not be debugged. But if the process is started by the debugger the process can be started with DEBUG_PROCESS meaning that both the new process and any child processes created will be debugged by the same debugger.

I have been locking for a way to change this DEBUG_ONLY_THIS_PROCESS flag since Application Inspector is able to attach to a process and I want it to monitor all child processes as well.

A couple of days ago I stumbled on a comment on a Microsoft descrition on that was new in Windows XP, talking about Dynamic Control over Debug-child Flag. The description did not describe how to change the flag so I had to investigate.

After some debugging of windbg and dbgeng.dll, that can change the setting using the command .childdbg I found the kernel call to do that I want. It's the undocumented NtSetInformationProcess that is able to change the debug flags.

Here is the code to set the flag.

//// Process options.//

// Indicates that the debuggee process should be// automatically detached when the debugger exits.// A debugger can explicitly detach on exit or this// flag can be set so that detach occurs regardless// of how the debugger exits.// This is only supported on some system versions.#define DEBUG_PROCESS_DETACH_ON_EXIT 0x00000001// Indicates that processes created by the current// process should not be debugged.// Modifying this flag is only supported on some// system versions.#define DEBUG_PROCESS_ONLY_THIS_PROCESS 0x00000002

Wednesday, September 5, 2007

I have just finished assembling my new workhorse in the home office. I have a server running VMware mostly and it has been a little slow lately. But now after upgrading motherboard, CPU and memory it's a lot quicker.

The spec. for the new machine:

AMD Athlon X2 6000+

aBit AN-M2HD motherboard

2GB Crucial BallistiX PC640

To keep the system quiet I also ordered a Thermaltake BigWater 745 water cooling system. The picture shows everything installed in the case.

Because the case has an unusual design with the drive bay for up to 4 hard disks in the bottom of the case I had to place the water pump on the top instead. This does the noise of the pump a little bit louder, but not too much. I have not done any real tests of the cooling yet, more information on the resulting temperatures will follow on this blog.

For the new system I decided to change the host OS as well. I'm now running Ubuntu 7.04 (Fieasy Fawn) amd64. To simplify the migration I installed Linux to a new disk and created a VMware machine from the old hard disk. To be able to boot the machine I had to change the newly created VMware machine to use IDE interface for the disk. This was a simple edit of two config files; first in the vmdk file the adapterType had to be changed to ide, and in the vmx file all scsi0 entries had to be changed to ide0. After the old machine was booted virtually I converted the machine to a standard file based VMware image using VMware Converter.

Wednesday, June 13, 2007

Since I'm mostly travelling around between my different customers my laptop is the only computer I have around. To setup test environments for the different projects I use the free VMware player and WMware server products to create virtual machines, in which I can test different solutions.

One of my last projects was to find a memory leak in a kernel mode driver. To do this I needed to do some kernel mode debugging again, something that normaly involves two computers connected by a serial cable. But not any more. It's a simple thing to setup a kernel mode debugging session using VMware.

First we need to get VMware to export a COM serial port to the host. This can be done through a named pipe and some lines added to the VMware configuration file for the virtual machine.serial0.present = "TRUE"serial0.fileType = "pipe"serial0.fileName = "\\.\pipe\com_1"serial0.tryNoRxLoss = "TRUE"serial0.pipe.endPoint = "server"

Now boot the virtual machine and select to boot into the DEBUG version. During the boot windows will stop and wait for the debugger. To start the debugger we give the arguments to connect to the named pipe that the VMware player now has created.windbg.exe -b -k com:pipe,port=\\.\pipe\com_1,resets=0"

The boot will stop on a breakpoint during bootup, just enter g and press enter to continue.

To shorten the round-trip then doing driver development it's very nice to be able to change the driver directly on the target machine. This is since all bugs in kernel mode ends up in a BSOD (Blue Screen of Death). To do this a VMware utility called DiskMount comes very handy. With this utility it's possible to mount the virtual machine hard disk on your host computer and change the driver before the next boot.

Tuesday, June 12, 2007

Anyone who has deployed any large application using Java Web Start 1.5 or 1.6 over a slow WAN or through some kind of SSL proxy has noticed the extreme number of connections that can be initiated during application startup. The first deploy of the application works as expected and all the JAR files is downloaded. But the sencond time the user clicks to start the application, Java Web Start will flood the network with connections to the server.

Investigation the problem revelas an interesting piece of code in the class com.sun.javaw.LaunchDownload and the method updateCheck, this function is called once for every JAR file in the JNLP description file. The code does the update check by starting a new thread and doing a HTTP request to the web server to check if the JAR file has been updated.This means that if we have a JNLP file with 200 JAR files, the code will start 200 threads, creating 200 individual connections to the server!

The solution can be found in the same function as well, as the first lines of the function reads: // no update check for versioned resource if (version != null) return;

This means that if we put version attributes on the JAR files we will not invoke the badly written code. To add the version attribute is simple, just add it to the JAR element of the JNLP file:<jar href="/application/foo.jar" version="”1.0” />

When Java Web Start finds this attribute on a JAR element in the JNLP file it will send this version string along with the GET request to the server. Like:GET /application/foo.jar?version-id=1.0

To handle this on the server we have two options, if we are running a J2EE environment the JDK contains a JNLP servlet that can respond to this request and also return the required x-java-jnlp-version-id custom header, or we could implement the same functionality in some other kind of server side language.

I choose to implement the JAR server in PHP/Apache since we have noticed that the J2EE container we are using is not very good at serving large amounts of data.

To have Apache invoke my script for every JAR file requested from the server, I added the following lines to the httpd.conf file.AddType application/java-archive .jar

Action application/java-archive /cgi-bin/jar_send.php

The script is very simple; we have chosen to store the versioned JAR archivesas /application/foo_x_y.jar for version x.y. This makes the script very simple to implement, and make deploying very simple as well. Another strategy could be to store a complete version of the application under /x.y/application/foo.jar and have all JAR archives in the JNLP file reference the same version.

Monday, May 21, 2007

Last week I helped a customer with a problem doing client authentication against a web-service. The connection did not work becuse the client software, implemented using JBoss was not sending in its client certificate during the handshake. The client certificate was issued by Verisign, witch uses an intermediate CA to issue the certificates.

The server side was using a Microsoft ISA 2004 server. We started with checking the list of trusted certificate issuers the server was sending out with the help of the openssl toolkit.

openssl s_client -host secure.customer.com -port 443

Look at the list after Acceptable client certificate CA names.We concluded that the server was only sending a list of self-signed root CA certificates. The server had a lot more CA certificates installed but only a subset was presented as acceptable client authentication CA's.

In Microsoft ISA 2004 you don't have any means of configuring the list of acceptable CA's so we had to look at the other side in the communication.

The client software is implemented using JBoss 4.0.5.GA and JBoss remoting 1.4.3.GA but the as we found out, the problem was a general java problem.

When requested to present a client certificate the Java SSL classes uses an interface called KeyManager to locate the correct credential to use. The default implementation SunX509KeyManagerImpl does a search through all PrivateKeyEntry elements found in the configured keystore. Then doing the search the class will match all certificates in the entry against the list of acceptable CA's.

To get client authentication to work with a client certificate issued by an intermediate CA we need to have the complete chain present in the PrivateKeyEntry in the keystore.

To update a keystore with the correct certificate chain, we can use the openssl toolkit again. First get hold of all certificates in PEM format. To convert a DER encoded certificate to PEM format use:

How this complete certificate chain can be imported into the java keystore using the standard keytool program. But first we need to know the alias of the key we are going to update. We can list the content of the keystore with:

keytool -list -keystore keystore-file

During the import of the certificate chain, keytool will check that the certificates match the private key, so it's should not be possible to corrupt the keystore. But as always backup the file if your production depends on it...

To import the chain, use:

keytool -import -keystore keystore-file -alias alias -file chain.pem

Keytool will ask if you trust the certificate issuer, just answer Yes.

We can now check the content of the keystore again and make sure that the complete chain is present with:

keytool -list -v -keystore keystore-file

This command will do a verbose listing of the keystore, with all certificates.

Thursday, April 12, 2007

In my MythTV frontend I use a compact flash card as boot device, making the frontend into a diskless, silent media player. To connect the CF card to the system I use an IDE2CF adapter.

One annoying problem is that during boot, I get a couple of seconds timeout and some error output on the console. I think this comes from the IDE2CF card not supporting DMA correctly. The output I get is:hda:hda: dma_timer_expiry: dma status == 0x21hda: DMA timeout errorhda: dma timeout error: status=0x58 { DriveReady SeekComplete DataRequest }ide: failed opcode was: unknown

I have searched the Internet and the only solution I have found said to include the ide=nodma commmand line parameter to the kernel, in the GRUB menu.lst file. That did not work, I still got the timeout.

I when decided to look into the source code directly, to try to see if I could find the error message and maybe see why the ide=nodma option was not working. I studied the code and found one interesting function. In the file ide-probe.c the code probes the IDE disks, and one call is to a function called ide_dma_check that probes the DMA capabilities of the drive. It seems that this ide_dma_check does it job and ignores the nodma command line option. My simple solution was to remove the call to ide_check_dma completely. I don't want DMA in my setup.

To patch your kernel you need to download the kernel source and the tools needed to build the new kernel.My whole MythTV system is built on debian, so your exact procedure may be different if you use a different distribution.

Just comment the call to hwif->ide_dma_check(driver) and the error message and startup timeout should go away. I admit that maybe the right solution is to look at the noautodma global variable, but this patch fixed my problem. // hwif->ide_dma_check(drive);

After a (long) while the compilation will be finished and you can pick up two new .deb packages under /usr/src. One package for the kernel image and one for kernel headers. These new packages can be installed onto the frontend with:#>dpkg -i linux-image-2.6-18-nodma-10.00.Custom_i386.deb

Thursday, March 29, 2007

Today I wrote a reporting tool for our Web 2.0 project. I wanted a simple solution that enabled the end customer to create his own reports based on the ones we creates during development.

To make the system flexible I used the Smarty template engine. Smarty works by compiling templates describing layout into PHP files that is when combined with data from an application into a presentation. The normal use of Smarty is to create HTML pages for viewing in a browser, but the code is well written and can be used in many more ways.

I also wanted the SQL queries to be configurable, to allow even more flexibility in the design of the reports. The solution was to use a feature in Smarty that is normally used to avoid hard coding in the templates, the config files. In my solution the report is a config file that specifies the content of the report. A simple report looks like this:

The application can easily build a list of all the reports in the system by looking at all the files *.rep in the reports directory, using the glob PHP function. The reports supports to be rendered in three different ways, screen, print or excel.

To generate the report, the PHP code fetches and executes the different queries configured in the report. Two different kinds of queries are supported, queries returning lists and queries returning a single value.

After all the data has been read in from the database, Smarty is called to render the report. The $show variable holds the type of report to generate; this could be screen, print or excel. This makes in possible to have some parts of the report generated the same way independently if the report is intended for the printer, screen or for Excel.

About Me

Stefan Gustafsson

Im running a small software consultancy firm and helping my customers design and implement solutions in the Internet era.
Expisoft is a joint venture with a couple of friends to create a software company selling good software, like the one we need and like ourself.